JOHANNESBURG (Reuters) - Five workers were trapped underground in a South African gold mine owned by Harmony Gold following an earth tremor, the mining company said on Friday.

South Africa-based Harmony said in a statement that rescue teams had been working to find the workers since the incident occurred at about 10.30 a.m. local time at its Kusasalethu mine near Cartonville, west of commercial hub Johannesburg.

South Africa is home to the world’s deepest mines where workers operate at depths of up to 4 km (2.5 miles) beneath the surface. Nevertheless, the industry has reduced the number of miners killed in mines, with a new record low of 73 registered last year compared with 77 in 2015.